1. Field of the Invention
This invention relates to laser scanning apparatus for photolithography of slotted mask color cathode ray tubes. Accordingly, it is a general object of this invention to provide new and improved apparatus of such character.
2. Description of the Prior Art
It is an object of this invention to provide new and improved means for shaping a beam from an argon ion laser and scanning the resultant beam across a photosensitive resist layer on the inside of the glass panel of a slotted mask cathode ray tube in order to expose the resist layer in a fashion consistent with the electron beam landing positions required in an operating cathode ray tube. Some suggestion has been set forth in U.S. Pat. No. 4,027,312, discussed in greater detail in the next heading, "Prior Art Statement".
Previous related art for the foregoing purpose, other than the '312 patent, included the use of a mercury arc lamp with a special quartz rod whose tip had been drawn into the shape of a wedge as a light source along with an aspheric lens juxtaposed between the source and the panel-mask assembly. The wedge shape of the rod (collector) tip was vital for the proper screening or exposure of the photoresist pattern in that the tip thus acted as a slit source of light for the slot apertures of the shadow mask. The wedged collector tip was aligned parallel to the slots of the shadow mask. The tip dimensions were chosen so that the bridges between the slots in the mask were not printed on the photoresist. Alternatively, the tip was moved along the direction of the edge of the wedge during exposure to print uniform stripes of photoresist on the panel. The aforementioned aspheric lens corrects the virtual location of the collector slit tip to position the photoresist stripes coincident with the electron beam landing positions in the CRT.
The subject matter described in U.S. Pat. No. 4,027,312 performs functions similar to the instant invention. For example, an argon ion laser is used as a source, a motor-driven assembly is used to scan the laser beam across the panel in a raster fashion and the function of virtual source location by means of galvanometer mirror scanners is employed. The optical system to be described differs significantly from the prior art and the control functions utilized in the following description are new.
3. Prior Art Statement
This prior art statement shall serve as a representation that the prior art listed herein includes, in the opinion of the applicants, the closest prior art of which they are aware. This statement shall not be construed as a representation that a search has been made or that no better art exists.
U.S. Pat. No. 4,053,905, issued Oct. 11, 1977 to John Schlafer, entitled "Optical Scanning Apparatus For Photolithography of a Color Cathode Ray Tube Having An Aperture Mask", relates to an optical scanning apparatus for use in manufacturing cathode ray tubes wherein a layer of a photosensitive material on the inner surface of a tube faceplate is exposed by scanning a light beam over an array of light transmitting apertures in a mask disposed adjacent to the layer of material on the faceplate. The apparatus includes:
(a) a light source for creating a light beam having a wavelength spectrum which exposes the photosensitive material, PA1 (b) means disposed in the path of the light beam for deflecting the light beam through an angle which is related to a predetermined angle of incidence that an electron beam has at each point on the aperture mask as it passes through the transparent regions of the mask in an operating tube, PA1 (c) optical means, operating on the deflected light beam, for imaging the point of deflection of the light beam substantially at the faceplate so that the light beam may be made to impinge on the mask with an angle of incidence related to that of an electron beam in an operating tube, the angle of incidence being obtained substantially without translation of the light beam at the faceplate, and PA1 (d) means for scanning the deflected light beam over the aperture mask in a predetermined fashion to expose the photosensitive material adjacent to all light-transmitting regions on the mask, the deflecting means being operative in synchronism with the scanning means to provide the light beam with the proper angle of incidence for each light-transmitting region on the mask. PA1 selecting a matrix of data points on the viewing screen of a cathode ray tube; PA1 altering the positional location coordinates of said light beam source of said optical scanning exposure apparatus to effect light beam impingement at each of said data points; PA1 recording said altered positional coordinates of said optical scanning exposure apparatus; PA1 constructing a cathode ray tube having a viewing screen structure with a field of phosphor elements fabricated in accordance with said altered position location coordinates of said optical scanning exposure apparatus; PA1 measuring the error of impingement of an electron beam on said elements of said phosphor field at said viewing screen of said cathode ray tube; PA1 varying said recorded altered positional location coordinates of said optical scanning exposure apparatus in accordance with said measured error of impingement; and PA1 submitting said varied positional location coordinates of said optical scanning exposure apparatus to a lens design program to provide lens manufacturing information. PA1 retrieving from said angle of incidence and scan rate memory means signals for altering the operation of said scan rate means to cause said horizontal and vertical light beam scanning means to provide overlapping adjacent horizontal scan lines and more uniform illumination of the photosensitive layer on the faceplate of the cathode ray tube.
U.S. Pat. No. 4,027,312, issued May 31, 1977 to John Schlafer et al., entitled "Optical Scanning Apparatus and Method for Manufacturing Cathode Ray Tubes", relates to an improvement in an optical scanning apparatus for manufacturing cathode ray tubes having a layer of photosensitive material disposed on the faceplate inner surface and exposed by scanning a light beam over an adjacent apertured mask wherein the optical scanning apparatus includes a light source provide a light beam of a wavelength which exposes the photosensitive material, means disposed in the path of the light beam for deflecting the light beam at an angle related to an angle of incidence of an electron beam in a cathode ray tube, means for imaging the deflected light beam at the faceplate of the cathode ray tube, and means for scanning the deflected light beam over the apertured mask in a predetermined fashion to expose the photosensitive material adjacent the apertures of the mask. The improvement comprises means for controlling the effective area occupied by the light beam at the scanning means to effect control of the size and shape of the exposed area of photosensitive material in relation to an associated aperture in the mask.
Various scanning exposure systems are known. In such a system, a small light beam is scanned over the aperture mask so as to expose the photosensitive material adjacent to the light-transmitting regions or apertures in the mask. For example, a scanning exposure system is described in the British Patent Specification No. 1,257,933. In this patent, a scanned laser beam is used in conjunction with an aperture mask and photosensitive material for delineating phosphor patterns on faceplates for color CRTs. However, this patent does not provide for correction of the inherent discrepancy between electron beam landings and phosphor locations.
Another scanning exposure system is described in the U.S. Patent to Geenen et al., No. 3,876,425. In this system, the effective light beam source is actually translated about a source plane to provide correlation between phosphor locations and electron beam landing locations. Such beam translation eliminates the need for the aspheric lens which is necessary in the non-scanning exposure system. In the system described in the Geenen patent, the effective light beam source is the center of a mirror which deflects the beam toward the faceplate. An optical system always insures that the beam from the actual source is always directed to the center of the scanning mirror. The scanning mirror is carried by an assembly that rotates the mirror about two orthogonal axes to provide scanning and that translates the mirror along two orthogonal axes to provide movement of the center of the mirror in the source plane. The optical system includes a plurality of mirrors, bearing assemblies and a telescoping member.
This system has limitations which render it less than suitable for use in a production environment for cathode ray tubes. First, a scanning exposure system must have accurate optical alignment characteristics, i.e., the ability to repeatedly position the light beam at a predetermined point on the faceplate. The mechanical and optical system described is of such a complicated nature that it is doubtful that such alignment characteristics could be obtained. More specifically, the large number of rotating parts and simultaneously rotating and translating parts of the system could result in misalignment with continued use as is necessary in a production environment. Furthermore, the feature of actually translating the effective light beam source in a plane adds complexity to the electronic system which is necessary to control the scanning and mirror translation functions. More specifically, each time the mirror is translated, the beam if not corrected by the scanning function, would impinge upon other than the desired faceplate location. Thus, the translating and scanning functions are interdependent.
Both the British Patent Specification No. 1,257,933 and U.S. Pat. No. 3,876,425 to Geenen are mentioned in both the above U.S. Pat. Nos. 4,053,905 and 4,027,312.
U.S. Pat. No. 4,030,790, issued June 21, 1977 to G. Norman Williams et al., entitled "Process for Fabricating Lenses for Manufacturing Cathode Ray Tube Screen Structures", in the field of manufacturing color cathode ray tube screen structures, relates to a lens fabricating process utilizing optical scanning exposure apparatus having a positionally locatable light beam source comprising the steps of:
U.S. Pat. No. 4,053,903, issued Oct. 11, 1977 to Thomas W. Schultz, entitled "Scanning Rate and Intensity Control for Optical Scanning Apparatus" relates to an improvement in a control system for use with an optical scanning exposure system in manufacturing cathode ray tubes having a faceplate with a layer of photosensitive material thereon. The optical scanning exposure system includes a light source with a wavelength spectrum for exposing the photosensitive material, means for scanning the faceplate with a light beam, and means for deflecting the light beam at an angle related to the angle of incidence of an electron beam in a cathode ray tube. The electrical control system includes an angle of incidence and scan rate memory means, a scan rate means for controlling scanning of the light beam, and an angle of incidence deflection control means for controlling the angle of incidence of the light beam. The improvement comprises means for controlling the integral with respect to time of the light beam intensity at each exposed region of photosensitive material on the faceplate of the cathode ray tube to provide a predetermined amount of exposure at predetermined positional locations across the surface of the faceplate.
U.S. Pat. No. 4,053,904, issued Oct. 11, 1977 to G. Norman Williams et al., entitled "Overlap and Overscan Exposure Control System" relates to an improvement in a method for controlling an optical scanning exposure system for exposing a photosensitive layer on a faceplate of a cathode ray tube wherein the electrical control system includes an angle of incidence and scan rate memory storage means, scanning means, and an angle of incidence control means and the method for controlling the optical scanning exposure system includes the steps of activating the scan rate means to cause light beam scanning of the faceplate of the cathode ray tube, applying signals representative of the positional location of a light beam to the angle of incidence and scan rate memory means to derive signals representative of the angle of incidence of an electrom beam, coupling the signals representative of the angle of incidence of an electron beam to said angle of incidence control means, and coupling signals representative of said desired rate of scan to said means for effecting horizontal and vertical scanning. The improvement comprises the added step of:
U.S. Pat. No. 4,053,906, issued Oct. 11, 1977 to Thomas W. Schultz, entitled "Control System for a Optical Scanning Exposure System for Manufacturing Cathode Ray Tubes" relates to a control system in which there is provided a memory storage device for storing information representative of the proper angle of incidence of a light beam at a matrix of positional locations on the faceplate of the cathode ray tube and of the rate of scan of the light beam from one positional location to the next. The encoder provides horizontal and vertical light beam scan position information into the (memory) storage device. A scan rate device, responsive to the scan rate and position information in the memory storage provides signals for controlling the rate of light beam scanning. Further, an angle of incidence control device, responsive to angle of incidence and position information from the memory storage, provides electrical signals for the galvanometers which control the angle of incidence deflecting mirrors.
U.S. Pat. No. 4,050,081, issued Sept. 20, 1977 to Thomas W. Schultz, entitled "Exposure Area Control for an Optical Scanning System for Manufacturing Cathode Ray Tubes" relates to an improvement in a control system for use with an optical scanning exposure system in manufacturing cathode ray tubes having a faceplate with a layer of photosensitive material thereon, the optical scanning exposure system includes a light source with a wavelength spectrum for exposing the photosensitive material, means for scanning the faceplate with a light beam, and means for deflecting the light beam at an angle related to the angle of incidence of an electron beam in a cathode ray tube. The electrical control system includes an angle of incidence and scan rate memory means; a scan rate means for controlling scanning of the light beam, and an angle of incidence control means for controlling the angle of incidence of the light beam. The improvement comprises means for providing a source of signals for combination with a signal from said angle of incidence control means and coupled to said angle of incidence deflector means to cause movement of the effective light beam source in a source plane and provide an increased area of partial exposure and a decreased area to full exposure of said faceplate whereby the exposure area size and shape is controlled.
Various of the above-identified patents have been assigned as follows:
______________________________________ U.S. Pat. No. Assignee(s) ______________________________________ 4,027,312 GTE Laboratories Incorporated GTE Sylvania Incorporated 4,030,790 GTE Sylvania Incorporated 4,050,081 GTE Sylvania Incorporated 4,053,903 GTE Sylvania Incorporated 4,053,904 GTE Sylvania Incorporated 4,053,905 GTE Laboratories Incorporated 4,053,906 GTE Sylvania Incorporated ______________________________________
Both GTE Laboratories Incorporated and GTE Sylvania Incorporated are majority owned subsidiaries of General Telephone and Electronics Corporation.